Long live the LHC

Technology is always being improved and replaced. How does this affect immense, international, collaborative projects like the Large Hadron Collider?

 Illustration by Simona Seizova

Illustration by Simona Seizova

It seems that each new week begins with an announcement from one company or another about their latest and greatest technology or product. Mobile phones, computers, cameras, mobile apps and transportation, all under the relentless march of technological advancement. When does technology become old? What happens to it once it is replaced?

Early mobile phones were so large that they had to be carried about in dedicated briefcases. As the technology was refined, they shrank to the size of your average house brick, then to their modern dimensions. Our phones are becoming outdated much quicker than we’d like, but what happens when technological progress overtakes current technology and requires expensive, international projects to be replaced?

Take the Large Hadron Collider at CERN in Switzerland. A large, multinational collaboration where billions of dollars have been spent to investigate our universe. But what happens once the physics outstrips the capabilities of the LHC? Will it ever become obsolete, or will it simply fall from the forefront of particle physics research? 

Particle physics investigates the smallest components that make up matter: the particles that comprise atoms. The idea that matter is made up of smaller particles has existed since around the 5th century BC. More recently, during the early 20th century, as technology developed, new experiments provided the evidence needed to show the smallest particles of our universe. The structure of the atom (that it is mostly empty space with a centralised mass) was demonstrated by Ernest Rutherford in the early 1900s; since then we have continued to refine our understanding to smaller and smaller levels. As the technical skills and capabilities of engineers has improved, so has our understanding of the infinitesimal components of the universe.

The jewel of modern particle physics is undoubtedly the Large Hadron Collider (LHC). This colossal ring, with a circumference of 27km, is located under the European Alps between France and Switzerland. Though somewhat underwhelming in appearance, those tubes of the LHC that stretch off into the distance, curving slightly as they become a distant point, house some of the world's most powerful tech. High energy particles are accelerated and guided around this ring at close to the speed of light by superconducting electromagnets. There are several different types of magnets all working together to accelerate the particles and guide them to collide. The magnets must be kept at -271.3ºC, only 2º above absolute zero, the coldest theoretical temperature. Within the ring itself, the particles are travelling through an ultrahigh vacuum. The biggest operational vacuum in the world is emptier than interstellar space.

Discoveries made at the LHC have resulted from the collaboration of the best engineers and pioneering physicists. Perhaps the most well-known of these discoveries is of the Higgs Boson on 4 July 2012. Named after Scottish theoretical physicist Peter Higgs, who first predicted its existence in the 1960s, a Higgs Boson is a particle that exists in a quantum state of excitation — simply put, more than one of these particles can occupy a single point at any given time, unlike matter, which cannot. When there are many Higgs Bosons grouped together, they generate a Higgs field, which is what gives particles their mass.

The Higgs Boson belongs to a theoretical model of particle physics called the Standard Model, which describes the fundamental structure of matter in a series of eloquent equations — what everything is made of and how it is held together. Despite being our most complete understanding of the known universe there are things that are yet to be explained: the lack of antimatter in our universe, the unusually small mass of the neutrino, and why gravitational forces are relatively weak.

Scientists predict that some of the gaps remaining in the Standard Model can yet be filled in by the technology available at the LHC. Over the next 5 to 10 years, additional evidence of the Higgs Boson is expected, as well as extensions of the Standard Model involving particles known as heavy W and Z gauge bosons, which are responsible for weak nuclear forces. Historically, experimental technology becomes obsolete when we have exhausted all potential avenues of experimentation.

It is difficult to predict the direction particle physics will take in the future. It largely depends on whether the LHC makes any discoveries that fall outside of the Standard Model. It also depends on which of the following super colliders proposals get developed and built. Scientists absolutely want to squeeze every last drop of unique experimental data from the LHC before moving on to building its successor.

Sizing up the competition

Over the next 30 years or so, we can expect to see fervent competition between countries to host the next super collider. There has been a proposal from Japan to host the International Linear Collider, which, at 31km in length, would smash together electrons and positrons. Collisions between these particles are very clean and produce very little interfering debris. This is because positrons and electrons are fundamental particles — they are not made up of smaller particles. Compared with protons, which are quite messy due to being composed of many smaller particles, the electron-positron collisions can be conducted to a much greater accuracy than can be currently carried out at the LHC. We might get our first glimpse at the mysterious (and somewhat ominously named) dark matter.

China is also chomping at the bit to host an electron-positron collider and a proton collider, which could be anywhere from 50km to 100km in length. China’s plan is to build the electron-positron collider and then incorporate the proton-proton smasher, greatly reducing the combined cost — essentially gaining two colliders for the cost of one and a half. The colliders would be focused on the precision measurement of the Higgs particles and resulting fields. As with the electron-positron collider proposed by Japan, the electron-positron ring has much greater potential for accuracy and detection of new particles, whereas smashing protons together is a bit like cutting a cake with a sledgehammer.

Finally, there is the current home of modern particle physics: CERN. Their competing proposal is for a proton collider that would smash protons together at energies seven times higher than those possible at the LHC. This collider comes in as the longest of the three proposed in the form of a ring at 100km in circumference.

In reality, it is unlikely that all three of these proposals will be carried out — the world just doesn’t have enough cash. If China’s proposal were to go ahead, it would strengthen Japan’s argument for the International Linear Collider whilst simultaneously soaking up international funding. The proton-proton collider proposed by CERN may come a bit too late, with the work getting off the ground in the mid-2030s.

Super colliders must be built with a certain flexibility; to be able to justify their expense, they need to accommodate a range of experimental designs. The future of particle physics may not be all about building bigger and more powerful accelerators — similar to the evolution of mobile phones, particle physics colliders may become smaller before getting larger again.

Using AWAKE technology, which stands for Proton Driven Plasma Wakefield Acceleration Experiment, CERN is aiming to make accelerators smaller. These 'tabletop' accelerators need the attention of only tens of people, rather than tens of thousands. Costing merely a fraction of what it would take to build a super collider, these instruments would be within the financial reach of most universities.

The discoveries that are yet to be made at the LHC will have a major impact on the direction that particle physics will take. Until they are made it is tricky to pin down which proposal will replace the LHC and just how long it will take to do so. The rate at which these technologies age and are replaced is much slower than your mobile phone (thankfully) and it is likely that there will be some overlap between the operation of the LHC and its successor. Continuing upgrades to the LHC will further blur the lines between successive collider generations.

Certainly by the 2030s, more powerful and accurate accelerators and colliders will be under construction, long before the LHC takes a well-earned retirement and a step back from the frontiers of particle physics. Until then, it will continue to be the leader of the proton smashing world, pushing the limits of modern particle physics. 

Edited by Bryonie Scott